1. Field of the Invention
This invention relates to the prevention, reducing the formation or treatment of restenosis.
2. Description of the Sate of the Art
Percutaneous transluminal coronary angioplasty (PTCA) is a procedure for treating heart disease. A catheter assembly having a balloon portion is introduced into the cardiovascular system of a patient via the brachial or femoral artery. The catheter assembly is advanced through the coronary vasculature until the balloon portion is positioned across the occlusive lesion. Once in position across the lesion, the balloon is inflated to a predetermined size to radially compress against the atherosclerotic plaque of the lesion to remodel the vessel wall. The balloon is then deflated to a smaller profile to allow the catheter to be withdrawn from the patient's vasculature.
A problem associated with the procedure includes formation of intimal flaps or torn arterial linings that can collapse and occlude the conduit after the balloon is deflated. Moreover, thrombosis and restenosis of the artery can develop over several months after the procedure, which can require another angioplasty procedure or a surgical bypass operation. To reduce the partial or total occlusion of the artery by the collapse of arterial lining and to reduce the chance of the development of thrombosis and restenosis, a stent is implanted in the lumen to maintain the vascular patency. Stents are scaffolding structures, usually cylindrical or tubular in shape, functioning to physically hold open, and if desired, to expand the wall of the passageway. Typically stents are capable of being compressed for insertion through small lumens via small catheters, and then expanded to a larger diameter once at the desired location.
To treat the damaged vasculature tissue and further fight against thrombosis and restenosis, there is also a need to administer therapeutic substances to the treatment site. For example, anticoagulants, antiplatelets and cytostatic agents are commonly used to prevent thrombosis of the coronary lumen, to inhibit development of restenosis, and to reduce post-angioplasty proliferation of the vascular cells, respectively. To provide an efficacious concentration to the treated site, systemic administration of the medication can produce adverse or toxic side effects for the patient. Local delivery is a highly suitable method of treatment in that smaller levels of medication, as compared to systemic dosages, are concentrated at a specific site. Local delivery produces fewer side effects and achieves more effective results.
In addition to providing mechanical functionality, stents are being modified to provide biological therapy. One method of medicating stents involves the use of a polymeric carrier coated onto the body of the stent. A polymer dissolved in a solvent, and a therapeutic substance added thereto, is applied to stent and the solvent is removed to form the coating. Subsequent to the implantation of the stent, the medication is released from the polymeric coating. Although drug eluting vascular stents have illustrated significant results for the treatment of restenosis, there is a need for improved methods of the treatment of this condition.